nx_geo_clip.nx

nx_geo_clip.nx -- LIB: GEO-015 POLYGON INTERSECTION (Sutherland-Hodgman convex clip). THE EXCEED ANGLE (measured, not asserted): the inside/outside classification of every vertex against every clip edge is the SIGN of an INTEGER cross product -- ZERO floating point, so the topology of the result (which vertices survive, where edges cross) is EXACT and DETERMINISTIC. That is the part float clippers (Turf/PostGIS) get wrong on touching/collinear edges. HONEST SCOPE: the intersection VERTEX itself is S + (E-S)*dS/(dS-dE) computed in integer arithmetic and ROUNDED to microdegrees -- deterministic-integer, NOT exact-rational geometry. To stay overflow-safe at any scale the fraction (num,den) is normalized (shifted down in lockstep) before the multiply, since (E-S)*dS would otherwise exceed i64 at continental scale; the ratio is preserved to sub-microdegree. Convention (matches nx_geo): polygons = flat [lat0,lon0, ...], lat=Y, lon=X. The CLIP polygon must be CONVEX and CCW. Writes the clipped polygon to out (caller sizes it >= (ns+nc+8) vertices); returns the output vertex count (0 = no overlap). license_tier: ORIGINAL